1. Field of the Invention
The present invention relates to new radioactive iodine-125 miniature radiation sources (seeds) comprising a radioactive carrier matrix which consists of a porous and mechanically stable inorganic material, the pores of which contain inorganic insoluble iodide-125, and which is enclosed within a capsule made of a corrosion-resistent and body-compatible material or which is coated with such a material. The iodine seeds according to the present invention further may contain (a) usual X-ray marker(s). Another object of the present invention are methods for manufacturing said novel iodine-125 seeds.
Radioactive implants are used in tumour therapy in order to minimize surgical intervention into the patient. They may further be used to prevent the emergence of metastases or in post-operative tissue irradiation.
There are three basic types of irradiation therapy:
1. the interstitial therapy in which the radiation sources are implanted into the tissue to be treated;
2. the intracavitary therapy in which the radiation sources are inserted into a cavity of the human body by means of an applicator in order to expose the surrounding tissue to irradiation;
3. the intraluminal therapy in which the radiation sources are inserted into blood vessels by means of a catheter in order to expose the inner wall of the vessel or the surrounding tissue to irradiation.
For a long time, the exposure of tumours to local irradiation by using interstitial implants has been in common practice. Such method of treatment allows very precise dosing and restricting the treatment to a small area, thus minimizing the irradiation influence on healthy tissue.
The radiation energy of the iodine 125 isotope is appropriate for interstitial brachytherapy. Due to the low gamma energy level and the short half-life value of iodine 125, seeds doped with it may remain in the tissue as permanent implants without destroying healthy tissue. Also, there is no risk for medical staff and other persons being in contact with the patient.
The seeds have to be designed so as to allow a fast and simple insertion of the implants into the tissue to be treated. A common insertion technique uses hollow chamber needles to place the desired number of seeds into the tissue and then to retract the needle.
X-ray and ultrasonic techniques are used to identify the seeds in the body and to indicate their position. For this reason, so-called xe2x80x9cmarkersxe2x80x9d are integrated into the seeds, or a design is chosen which enables ultrasonic displaying. These markers are made of materials having a high density as for instance gold, silver, platinum, lead or iridium. They may have different shapes and sizes which depend both on the shape and the size of the radioactive carrier and on the requirements of the imaging and may be shaped as e.g. balls, tubes, wires. Further, it is known that the ultrasonic visualisation may be improved by roughening the surfaces, especially the metallic surfaces, for better reflection (etching).
2. Description of the Related Art
The prior art describes a great number of seeds which can be used as radiation sources in brachytherapy, e.g. in the U.S. Pat. No. 5,405,165 (Carden), U.S. Pat. No. 5,354,257 (Roubin), U.S. Pat. No. 5,342,283 (Good), U.S. Pat. No. 4,891,165 (Suthanthiryan), U.S. Pat. No. 4,702,228 (Russel et al.), U.S. Pat. No. 4,323,055 (Kubiatowicz), U.S. Pat. No. 3,351,049 (Lawrence) and WO 97/19706 (Coniglione). Iodine-125 seeds are disclosed in Lawrence, Kubiatowicz, and Suthanthiryan.
The iodine-125 seeds described in U.S. Pat. No. 4,323,055 (Kubiatowicz) contain a radioactive iodine layer on the surface of a matrix, which is in a preferred embodiment a silver rod which functions both as the active support and as the x-ray marker. Such seeds are manufactured, for example, by using a chemical reaction to transform the silver surface of the silver rod to silver chloride. The exchange of the chloride ion is implemented in a gaseous atmosphere so that silver iodide is chemically bound on the surface. Seeds produced in this manner tend to produce an asymmetric radiation field. Furthermore, the radiation is to a high degree self-absorbed by the silver rod. In this case, to ensure the therapeutically necessary amount of radiation more isotope must be added, i.e., in terms of isotope utilization, source production is less efficient and more costly. Further, the abrasion resistance of the silver rod with respect to the radionuclid is not statisfactorily.
Lawrence (U.S. Pat. No. 3,351,049) describes seeds with radioactive iodine-125 dispersed in an organic polymer, e.g. a nylon filament. Due to the high volatility of elemental iodine which is used in this design a mass production of seeds seems to be not possible.
The seeds described by Suthanthiran in U.S. Pat. No. 5,163,896 contain a metallic substrate which is coated with a radioactive-absorbing material comprising poly (amino acids). In U.S. Pat. No. 4,994,013 the seeds also contain a metallic substrate which is coated with carbon or active charcoal. Both designs are based on a coated metallic rod substrate which has similar disadvantages as described above for the silver rods reported by U.S. Pat. No. 4,323,055 (Kubiatowicz). The radiation is to a high degree self-absorbed by the metallic substrate.
It is an object of the present invention to provide novel iodine-125 miniature radiation sources which meet all requirements of interstitial therapy and do not have the drawbacks described above. It is the object of the present invention to easily and automatically manufacture iodine 125 seeds in large amounts which provide a good imaging in ultrasonics and fluoroscopy, which matrixes do have a good abrasion resistance and a homogenous radiation dose distribution.
This object of the present invention is achieved by radioactive iodine-125 seeds comprising a radioactive carrier matrix which is enclosed in a corrosion-resistent and body-compatible material, which is transparent for the emitted radiation and resistant to said radiation, wherein the carrier matrix consists of a porous and mechanically stable inorganic material, the pores of which contain inorganic insoluble iodide-125. The inorganic carrier matrix may be encapsulated or coated with the corrosion resistant and body-compatible material.
Physiologically tolerable materials which are suited for encapsulation or coating of the radioactive matrices are well known in the art. They may be composed of a resistant human tissue-compatible metal which also has low atomic weight to minimize X-ray shielding such as e.g. titanium or other corrosion-resistent metal alloy such as e.g. stainless steel. Further, they may be composed of a resistent human tissue-compatible metal compound (using reactive nitrogen, oxygen, methane, or carbon monooxide gases during coating to form carbides, nitrides, or carbonitrides of transition metals or other metals) such as titanium carbide, titanium nitride, titanium carbonitride, titanium aluminium nitride, zirconium nitride and hafnium nitride.